Coasts

• How are waves formed?

  Form due to wind blowing across the surface of the sea. The wind pulls the surface through friction and creates ripples that increase in height as they travel towards the beach
• Two types of waves

  Constructive - Strong swash, weak backwash. Low wave height. Low frequency. Deposits material on the beach

  Destructive - Strong backwash, weak swash. High wave height. High frequency. Erodes the beach and overtime wears it away
• What does the size of a wave depends on?

  The strength of the wind

  How long the wind has been blowing for

  Water depth

  Fetch - the distance the wave has travelled from its starting point
• The 5 erosional processes on a coast

  Hydraulic Action

  Abrasion

  Attrition

  Solution

  Corrasion
• Hydraulic Action


  The sheer power of the waves as they smash against the banks of the river. This cracks in the rock and eventually the rock breaks apart and collapses, expanding the channel
• Abrasion


  Rocks scrape and bang against the sides of the river wearing away the channel gradually (like sandpaper on wood)
• Attrition


  Rocks and pebbles hit each other wearing each other down becoming smaller eventually. This doesn't change the shape of the channel
• Solution (erosion)


  When the acidity of the water dissolves certain types of rocks e.g. limestone and chalk
• Corrasion


  Sand and pebbles picked up by the sea are hurled against cliffs causing the cliffs to be eroded
• What are the erosional landforms on a headland?

  Cave - cracks are formed in the headland due to erosion, as these cracks continue to open it becomes a cave

  Arch - the cave largens and breaks through the headland meaning you can see through it unlike a cave

  Stack - erosion widens the base of the arch and the roof eventually gets too heavy and collapses leaving a stack

  Stump - the stack is undercut at the base until it collapses and forms a stump

  
• Wave-cut platform

  • The sea attacks the base of the cliff and erodes , creating a notch
  • As the notch gets deeper the cliff becomes unstable and collapses through mass movement
  • The backwash carries the eroded material away leaving a wave-cut platform at the bottom of the cliff

  
• The 5 transportation processes along a coast?

  Longshore drift

  Traction

  Suspension

  Solution

  Saltation
• Longshore drift

  The process of sediment being carried by waves along the coastline is called longshore drift. Waves approach the coast at the same angle as the direction of the prevailing wind. The swash will carry the material at the angle of the prevailing wind. The backwash then flows the material directly down to the sea due to gravity. The process repeats itself along the coast in a zigzag motion.

  
• Traction


  Big rocks that roll across the sea bed
• Suspension


  Small rocks light enough to float within the water
• Solution (transport)


  Dissolved rocks e.g. limestone and chalk are carried in a solution
• Saltation


  Rocks too heavy to be suspended that bounce across the sea bed
• Depositional Landforms

  Beaches

  Spits

  Bar

  Sand dunes
• Beaches

  Large deposits of sand caused by constructive waves hitting a coastline. Normally have berms (elevated land where high tide reaches and deposits sand and materials leaving a taller piece of land)
• Spits

  A long narrow strip of land formed due to deposition. Longshore drift occurs but as the waves lose energy they deposit their sediment. Hooked ends can form if the direction of prevailing wing changes. Waves cannot get past the spit, therefore the water behind a spit is very sheltered. Alluvium is deposited here to form salt marshes or mud flats.
• Bar

  Formed when a spit can grow across a bay, joining two headlands together. This cuts of seawater from the bay and the area which was once a bay is now a shallow area of water called a lagoon. Lagoons do not last forever and may be filled up with sediment.

  
• Sand dunes

  Occur when prevailing winds blow sediment to the back of the beach. There are different types of sand dunes, the name they're given depends on their stage of development and position on the beach
• Different types of sand dunes

  Embryo dunes - Found in the upper beach where sand starts to accumulate around a small obstacle

  Yellow dunes - As more sand accumulates, vegetation may develop on the upper and back dune surfaces which stabilises the dune

  Grey dunes - Sand develops into soil as vegetation growing there dies adding nutrients to the sand

  Dune slack - Water is trapped between hollows between dunes. This water allows the growth of moisture-loving plants

  Health and woodland - Greater nutrient content in the sandy soils means less brackish plants can thrive. Trees will also grow.
• Weathering


  The breakdown and decay of rocks in-situ (where they originally lie)
• What is mechanical weathering?

  Mechanical weathering is the breakdown of rocks due to physical processes without chemical changes taking place.

  An example is freeze-thaw when water enter the cracks of a rock and freezes overnight during the winter. When the water freezes it expands by around 10% increasing the pressure acting on a rock, cracks develop further weakening the cliff making it more vulnerable to erosion
• What is chemical weathering?

  Chemical weathering is the breakdown of rocks and minerals through chemical reactions.

  The most common example is carbonation where acid rain reacts with calcium carbonate in rocks which forms a chemical compound which can easily dissolve the rock
• What is biological weathering?

  Biological weathering is the breakdown of rocks and minerals by living organisms e.g. bacteria, plants and animals
• Mass movement


  The downhill movement of sediment that moves because of gravity
• 4 types of mass movement

  Rockfalls - bits of rock fall off sloped cliffs, usually due to the rock being exposed to freeze-thaw weathering.

  Landslide - water between sheets of rock (bedding planes) and the cliff reduces friction making it easier for large blocks of rock slide downhill.

  Mudslide - saturated soil (soil filled with water) flows down a slope like a fluid

  Rotational Slip - Also known as slumps. Saturated soil slumps down but instead of going down the hill like a mudslide, chunks of rock and soil slip creating steps (which are called heads) down the hill

  
• Three types of coastal management

  Hard engineering - uses man-made structures to reduce or halt erosion. Are effective but high-cost

  Soft engineering - uses more natural materials in a more environmentally friendly way. Complements the environment unlike hard engineering

  Managed retreat - erosion is allowed to carry on. Instead, the rate of erosion is monitored and ways of adapting to it are put in place for the future. This is becoming more popular as the cost of hard and soft engineering is too much for local councils
• Soft engineering (coasts)

  Dune nourishment - Marram grass planted on sand dunes stabilises the dunes and helps to trap sand to build them up.

  • Relatively cheap and maintains a natural-looking coastline.
  • Can be damaged in a storm and planting is time-consuming.

  Beach nourishment - Sand is pumped onto an existing beach to replace material lost through erosion and transportation.

  • Maintains the beach which is a major tourist attraction and blends in with the existing beach
  • Needs to be constantly replaced.
• Hard engineering (coasts) pt1

  Groynes - wooden or rock structures built out at right angles into the sea that trap sediment

  • Builds up the beach - which encourages tourism and is cost effective
  • By trapping sediment it starves beaches further down the coastline, increasing rates of erosion elsewhere.

  Sea walls - curved concrete walls that absorb and reflect wave energy

  • Sea walls usually have promenades (paths) so people can walk along them and are effective at protecting the base of the cliff.
  • Waves can break down and erode the sea wall also they're expensive
• Hard engineering (coasts) pt2

  Rock armour - large rocks placed at the foot of a cliff that absorb the waves energy.

  • Cheaper than a sea wall - cost effective and easy to maintain.
  • They look different to the local geology, as the rock has been imported from other areas, they're also expensive to transport.

  Gabions - Rocks are held in mesh cages and placed in areas affected by erosion.

  • Cheap and absorbs wave energy.
  • Not very strong and looks unnatural.